Mpls L3Vpn Packet Forwarding - HP 10500 Series Configuration Manual

From the egress PE to the remote CE:
3.
After receiving the VPN-IPv4 routes, the egress PE compares their export target attribute with the
local import target attribute, and, if they match, adds the routes to the routing table of the VPN
instance. Then the egress PE restores the VPN-IPv4 routes to the original IPv4 routes and advertises
those routes to the connected CE through static routing, RIP, OSPF, IS-IS, EBGP, or IBGP.

MPLS L3VPN packet forwarding

In a basic MPLS L3VPN (within a single AS), a PE adds the following information into VPN packets:
• Outer tag—Identifies the public tunnel from the local PE to the remote PE. The public tunnel can be
an LSP, an MPLS TE tunnel, or a GRE tunnel. Based on the outer tag, a VPN packet can be
forwarded along the public tunnel to the remote PE. For a GRE public tunnel, the outer tag is the
GRE encapsulation. For an LSP or MPLS TE tunnel, the outer tag is an MPLS label.
Inner label—Identifies the remote VPN site. The remote PE uses the inner label to forward packets
•
to the target VPN site. MP-BGP advertises inner labels for VPN routes among PEs.
Figure 28 VPN packet forwarding
Site 1
2.1.1.1/24
1.1.1.2
As shown in
Site 1 sends an IP packet with the destination address 1.1.1.2. CE 1 transmits the packet to PE 1.
1.
PE 1 finds the matching VPN route based on the inbound interface and destination address of the
2.
packet, labels the packet with both the inner label and the outer tag, and forwards the packet to
the public tunnel.
P devices forward the packet to PE 2 by the outer tag. If the outer tag is an MPLS label, the label
3.
is removed from the packet at the penultimate hop. If the outer tag is GRE encapsulation, PE2
removes the GRE encapsulation.
PE 2 finds the matching VPN route according to the inner label and destination address of the
4.
packet, and then forwards the packet out of the interface to CE 2.
CE 2 transmits the packet to the destination through IP forwarding.
5.
When two sites of a VPN that are connected to the same PE communicate, the PE directly forwards
packets between the two sites through the VPN routing table without adding any tag or label.
For more information about GRE, see Layer-3 IP Services Configuration Guide.
CE 1
PE 1
Outer tag
Inner label
1.1.1.2
Figure 28, a VPN packet is forwarded from Site 1 to Site 2 using the following process:
P P
MPLS network
Inner label
1.1.1.2
90
Site 2
CE 2
PE 2
1.1.1.2/24
1.1.1.2